Problem 24 - A Complete Resource Book in Chemistry for JEE Main

Question

At \(15^{\circ} \mathrm{C}\), out of \(\mathrm{H}_{2}, \mathrm{CH}_{4}, \mathrm{CO}_{2}, \mathrm{NH}_{3}\), which gas will be adsorbed maximum by charcoal? (a) \(\mathrm{H}_{2}\) (b) \(\mathrm{CH}_{4}\) (c) \(\mathrm{CO}_{2}\) (d) \(\mathrm{NH}_{3}\)

Step-by-Step Solution

Answer

Ammonia ( \( NH_3 \) ) will be adsorbed the most by charcoal.

Step 1: Understanding Adsorption

Adsorption is a process where a solid holds molecules of a gas or liquid on its surface. It generally depends on the nature of the gas and the surface area of the adsorbent. In this case, charcoal is the adsorbent, and we need to determine which gas it will adsorb the most.

Step 2: Consider Essential Factors for Adsorption

The ability of a gas to be adsorbed is influenced by several factors, including molecular size, polarity, and critical temperature. Typically, larger molecular size and higher critical temperature lead to higher adsorption.

Step 3: Analyze Each Gas's Properties

- **Hydrogen (\(H_2\)):** Smallest molecule, non-polar, very low critical temperature.- **Methane (\(CH_4\)):** Non-polar, low critical temperature.- **Carbon Dioxide (\(CO_2\)):** Polar, higher critical temperature than \(H_2\) and \(CH_4\).- **Ammonia (\(NH_3\)):** Polar, highest critical temperature of all four gases, larger adsorption potential.

Step 4: Determine the Most Adsorbed Gas

Given the factors discussed, ammonia (\(NH_3\)) is likely to be adsorbed the most. It has a higher critical temperature and is polar, leading to stronger adsorption on a surface like charcoal.

Key Concepts

Critical Temperature

The critical temperature of a gas is a key factor in determining its adsorption onto solids like charcoal. This is the temperature above which the gas cannot be liquefied, no matter how much pressure is applied. Gases with higher critical temperatures are generally adsorbed more easily because they tend to have stronger intermolecular forces and exhibit more significant attractions to the adsorbent's surface.

When considering the gases from the problem, ammonia (1 ext{NH}_32) has the highest critical temperature compared to others like hydrogen (1 ext{H}_22), methane (1 ext{CH}_42), and carbon dioxide (1 ext{CO}_22). This higher critical temperature means 1 ext{NH}_32 has a greater tendency for adsorption, making it a prime candidate for maximum adsorption by charcoal under the conditions provided.

Molecular Polarity

Molecular polarity is another important factor when it comes to gas adsorption. A polar molecule has a partial positive charge on one side and a partial negative charge on the other, which enables it to interact with and adhere to surfaces more effectively than non-polar molecules.

In our example, ammonia (1 ext{NH}_32) and carbon dioxide (1 ext{CO}_22) are polar gases. These gases experience stronger van der Waals forces and are more likely to be adsorbed onto the surface of a material like charcoal. In contrast, hydrogen (1 ext{H}_22) and methane (1 ext{CH}_42) are non-polar and therefore have weaker interactions with the adsorbent. Consequently, among all the gases mentioned, polar gases, particularly ammonia with its high polarity and critical temperature, will be more readily adsorbed.

Adsorbent Surface Area

The surface area of the adsorbent is crucial in determining the extent of gas adsorption. A larger surface area provides more sites for gas molecules to adhere to, thus increasing adsorption. Charcoal, with its porous and expansive surface area, is highly effective at adsorbing gases.

When considering adsorption, the combination of a large surface area and the chemical properties of the gases, such as polarity and critical temperature, work together to enhance the process. Charcoal's extensive surface characteristics allow it to take full advantage of the polar properties and higher critical temperatures of certain gases, such as 1 ext{NH}_32. Therefore, the considerable surface area of charcoal, in conjunction with the adsorptive qualities of gases like ammonia, results in a maximized adsorption capacity.